Oilwell drilling and well completion operations use an assortment of chemical additives, including polymeric chemical additives, to provide various effects including higher viscosity to water and reduction of hydraulic friction in well pumping operations. The global expansion of hydraulic fracturing relies upon a dependable source of chemical and polymer additives in order to function. The present invention relates to a method and apparatus for blending water-soluble dry powdered chemical additives into fresh water or non-fresh water. Chemical products are used in drilling, completion and fracture operations to achieve many different functional outcomes. It is common for well service operators to use water-soluble and/or water-dispersible chemical additives in the form of liquid or powdered chemicals or liquid-powder suspensions for easier dispensing, metering and addition to water-based liquid systems. As an example, small size powdered polymers such as polymeric polyacrylamide friction reducers and other polymeric viscosity additives have been replaced in many well operations and treatment applications with oil-in-water emulsion-based products, which offer operators an easier and consistent addition of chemical additives into the working liquid. Liquid high molecular weight polyacrylamide polymers are delivered as water-in-oil liquid emulsion. The liquid polyacrylamide emulsions are typically made by polymerizing an acrylamide monomer in an oil consisting of a hydrocarbon containing emulsifying surface-active or other types of chemical agents to create an oil-in-water emulsion, with the active polymer contained within aqueous droplets evenly dispersed in an oil carrier. The polyacrylamide emulsion is dispersible in water. In order to function properly the polyacrylamide emulsion must first be inverted or “broken” through addition or dilution of water and strong agitation. As the polymer is already dissolved within the aqueous phase of the emulsion, maximum friction reduction and viscosity building performance is expected to occur much more rapidly than in the addition of a dry powder polymer product. The emulsion products are designed to be less active than powders resulting in more handling and freight associated with their use.
The invention is not limited to working solely with friction reducers and/or viscosity building polymers. A wide variety of chemical additives are commonly used in well drilling, completion and fracture operations. Just as with the friction and viscosity polymers, the other chemical additives are commonly delivered to well site as lower-activity water-soluble liquid products. There are measurable and meaningful cost-savings advantages to using powdered chemical additives versus using products delivered as liquids, such as lower handling and freight costs for delivery and storage at the well site. Additionally, liquid chemical products delivered to well site in bulk shipping containers are more susceptible to leakage or spillage than products delivered as powders. Liquid chemical spills create possible exposure issues to workers and environmental cleanup hazards.
Powders used in oil well operations have typically been delivered in bags of various volumetric amounts. The smaller size chemical powder bags are 50 pounds and 100 pounds, normally handled by workers, and poured directly into the liquid container equipped with mixing equipment, such as a rotating blending propeller or circulating pump system, or the powder is poured into an eductor style powder induction system in line with all or a portion of the liquid flowing through the eductor. When powder is added into a liquid blend tank there is a period of time required to sufficiently hydrate and dissolve the powder. The typical eductor device is based upon the Venturi principle where a pump pressurizes the liquid directed into the eductor. When the liquid exits the eductor orifice, it is released into a lower pressure environment which creates a vacuum in the body of the eductor, downstream of the eductor orifice. A powder is poured into an overhead receptacle above the eductor body, where it is drawn by gravity and the vacuum created from the pressurized flow of liquid through the eductor orifice into the eductor body where it combines with the liquid flow. There are several limitations associated with the use of this type of traditional eductor blending system. Manually pouring the powders into the eductor overhead receptacle can lead to premature liquid wetting causing plugging of the eductor suction section, resulting in inconsistent feed rate. Any disruption requires a system shutdown and maintenance to clear any blockage in the suction section of the eductor.
Further, the traditional powder eductor apparatus and blending methods require considerable operator effort to accurately meter powdered chemical products into a flowing liquid system. It is more common for the traditional eductor methods to involve batch addition of known weights of powders into a given volume of liquid rather than a dynamic addition of powder based upon moment-to-moment system requirements. The traditional eductor powder addition method makes it more difficult for operators to accurately meter powders into a continuous flow of liquid. This invention meets the need for a much improved, low cost, efficient, accurate method and apparatus for powder addition into a flowing liquid stream. The unique invention combines several techniques and apparatuses to make it possible to evenly disperse and dissolve powders into liquids in a continuous manner. The invention makes it much easier for operators working at well drilling, well completion, and well fracturing operations to use powdered chemical additives rather than liquid chemical additives in their liquid systems. The use of powder chemical additives offers a more safe, economical method of treating liquids and minimizes the potential for leakage of chemicals into the environment.
There are several commercial powder dispersion systems in the market used for dispensing and dissolving a range of powdered chemical products into water. The present invention provides an improved method and apparatus for adding powdered chemical additives and then blending the powder into water or other liquid at volume.
The addition of hydratable polymeric powders into water systems at high volumetric flow rates presents special problems for well service operators. If the powder is added too quickly it will only partially hydrate in the water or liquid, resulting in reduced product performance. Blending difficult-to-hydrate polymers at high addition rates into water and liquid systems places special challenges on powder addition and blending systems. The present invention overcomes these problems and is capable of high rates of addition of water-hydratable polymer powders, such as high molecular weight polyacrylamide friction reducers and other polymeric-type viscosity additives, into water systems without creating gelled “fish eyes” of agglomerated solids in the water or liquid. When hydratable polymer powders are highly hygroscopic and improperly dispersed, they tend to form small partially hydrated polymer particles encapsulated in highly viscous, partially hydrated gel. The existence of partially hydrated fish eyes in well service water or liquids is unacceptable for well site operations. Commercially available powder dispersion systems use high energy/shear dispersion mechanisms, liquid shearing pumps and/or centrifugal pumps, to prevent the hydratable powder from forming fish eyes. However, there are drawbacks to using high energy mixing systems. In the case of high molecular weight polymers which are used in water or liquid systems, the polymer can be mechanically sheared, damaging the physical characteristics and performance properties of the powder after it is solubilized into the water or liquid. This is especially true with viscosity building and friction reducing high molecular weight polyacrylamides in water.
The typical powder eductor mixer relies on the force and volume of liquid flowing through an internal eductor nozzle to create a negative pressure or vacuum immediately downstream of the point in which the liquid exits the nozzle. The vacuum is used to draw or suck the powder into the eductor body downstream of the eductor nozzle, and mix into the liquid flowing out of the eductor nozzle. In typical eductor operations the liquid is pumped through a nozzle of a smaller diameter than the pipe or liquid conduit, so it produces a release point of a high velocity stream of water or liquid. The high velocity liquid stream creates a lower pressure zone around the downstream end of a nozzle. The system relies on this low-pressure region to cause the powder to be drawn or sucked from a powder hopper or container located above the eductor body through a suction port into a mixing chamber in the downstream pipe section. The suction is created due to Venturi effect that results in a drop in pressure at the tip of the nozzle due to the fast flowing motive liquid which has gained kinetic energy due to the tapered shape of the nozzle.
Examples of prior art patents utilizing eductor or mechanical mixing processes include U.S. Pat. Nos. 9,782,732, 9,132,395, 8,905,627, 9,067,182, 8,322,911, US Pub. No. 2004/0256106, U.S. Pat. Nos. 5,328,261, 5,213,414, 4,603,156, 4,186,772, and 4,884,925.
Another limitation of current conventional mobile powder dispersion system involves the powder handling and feed system. Many of the commercial systems use gravity-fed hopper systems attached to a mechanical feed system, conveyor or screw feeder. Many of the chemical powders used in well operations are hygroscopic, water-seeking, and easily absorb atmospheric moisture, becoming “sticky” and difficult to flow. When working with friction reducing polyacrylamide-based polymers, the atmospheric moisture can cause the polymer to build up on the internal surface of handling equipment and hoses it comes in contact with, resulting in the interruption in normal operations.